[Unit Testing] Implement Missing Tests

[vikash018]

What is the requested change?

Description:
This issue is to track missing unit tests.

1. Incomplete tests

• xgb_classifier: to_json_multiclass.
• randomforest_classifier, decision_tree_classifier, xgb_classifier: multi-class classification tests.
• pls regression.

2. There are still some old tests that needs to be enhanced

• verticapy/tests/connect/test_connect.py
• verticapy/tests/datasets/test_datasets.py
• verticapy/tests/geo/test_geo.py
• verticapy/tests/hchart/test_hchart.py
• verticapy/tests/sql/test_sql.py
• verticapy/tests/stats/test_stats.py
• verticapy/tests/udf/test_udf.py
• verticapy/tests/utilities/test_utilities.py
• verticapy/tests/utils/os_utils.py

VerticaPy/verticapy/tests/vModel

• test_countvectorizer.py
• test_dummy_tree_regressor.py
• test_knn_regressor.py
• test_lof.py
• test_model_selection.py
• test_onehotencoder.py
• test_tools.py
• test_dbscan.py
• test_iforest.py
• test_kprototypes.py
• test_logistic_regression.py
• test_naive_bayes.py
• test_pca.py
• test_xgb_classifier.py
• test_balance.py
• test_delphi.py
• test_kde.py
• test_linear_svc.py
• test_mca.py
• test_nearestcentroid.py
• test_pipeline.py
• test_bisecting_kmeans.py
• test_dummy_tree_classifier.py
• test_knn_classifier.py
• test_linear_svr.py
• test_memmodel.py
• test_normalizer.py
• test_svd.py

3. Add missing tests whose coverage is less than 90%

• verticapy/_config/validators.py
• verticapy/_help.py
• verticapy/_typing.py
• verticapy/_utils/_display.py
• verticapy/_utils/_inspect_statistics.py
• verticapy/_utils/_logo.py
• verticapy/_utils/_map.py
• verticapy/_utils/_object.py
• verticapy/_utils/_parsers.py
• verticapy/_utils/_sql/_cast.py
• verticapy/_utils/_sql/_dblink.py
• verticapy/_utils/_sql/_display.py
• verticapy/_utils/_sql/_format.py
• verticapy/_utils/_sql/_merge.py
• verticapy/_utils/_sql/_random.py
• verticapy/_utils/_sql/_sys.py
• verticapy/_utils/_sql/_vertica_version.py
• verticapy/connection/connect.py
• verticapy/connection/oauth_manager.py
• verticapy/connection/read.py
• verticapy/connection/write.py
• verticapy/core/parsers/_utils.py
• verticapy/core/parsers/all.py
• verticapy/core/parsers/csv.py
• verticapy/core/parsers/json.py
• verticapy/core/string_sql/base.py
• verticapy/core/tablesample/base.py
• verticapy/core/vdataframe/_aggregate.py
• verticapy/core/vdataframe/_corr.py
• verticapy/core/vdataframe/_fill.py
• verticapy/core/vdataframe/_filter.py
• verticapy/core/vdataframe/_io.py
• verticapy/core/vdataframe/_machine_learning.py
• verticapy/core/vdataframe/_math.py
• verticapy/core/vdataframe/_multiprocessing.py
• verticapy/core/vdataframe/_pivot.py
• verticapy/core/vdataframe/_plotting.py
• verticapy/core/vdataframe/_plotting_animated.py
• verticapy/core/vdataframe/_read.py
• verticapy/core/vdataframe/_rolling.py
• verticapy/core/vdataframe/_scaler.py
• verticapy/core/vdataframe/_sys.py
• verticapy/datasets/generators.py
• verticapy/jupyter/_javascript.py
• verticapy/jupyter/_widgets.py
• verticapy/jupyter/extensions/chart_magic.py
• verticapy/jupyter/extensions/sql_magic.py
• verticapy/machine_learning/metrics/classification.py
• verticapy/machine_learning/model_selection/hp_tuning/cv.py
• verticapy/machine_learning/model_selection/hp_tuning/param_gen.py
• verticapy/machine_learning/model_selection/hp_tuning/plotting.py
• verticapy/machine_learning/model_selection/kmeans.py
• verticapy/machine_learning/model_selection/statistical_tests/ols.py
• verticapy/machine_learning/model_selection/statistical_tests/tsa.py
• verticapy/machine_learning/model_selection/variables_selection.py
• verticapy/machine_learning/vertica/automl/clustering.py
• verticapy/machine_learning/vertica/automl/dataprep.py
• verticapy/machine_learning/vertica/automl/supervised.py
• verticapy/machine_learning/vertica/decomposition.py
• verticapy/machine_learning/vertica/feature_extraction/text.py
• verticapy/machine_learning/vertica/model_management.py
• verticapy/machine_learning/vertica/neighbors.py
• verticapy/machine_learning/vertica/pipeline.py
• verticapy/machine_learning/vertica/pmml/base.py
• verticapy/machine_learning/vertica/preprocessing.py
• verticapy/machine_learning/vertica/tensorflow/base.py
• verticapy/machine_learning/vertica/tensorflow/freeze_tf2_model.py
• verticapy/machine_learning/vertica/tsa/base.py
• verticapy/machine_learning/vertica/tsa/ensemble.py
• verticapy/mlops/model_tracking/base.py
• verticapy/performance/vertica/qprof.py
• verticapy/performance/vertica/qprof_interface.py
• verticapy/performance/vertica/qprof_utility.py
• verticapy/performance/vertica/tree.py
• verticapy/pipeline/_ingest.py
• verticapy/pipeline/_transform.py
• verticapy/pipeline/parser.py
• verticapy/plotting/_highcharts/acf.py
• verticapy/plotting/_highcharts/bar.py
• verticapy/plotting/_highcharts/barh.py
• verticapy/plotting/_highcharts/base.py
• verticapy/plotting/_highcharts/heatmap.py
• verticapy/plotting/_highcharts/machine_learning/pca.py
• verticapy/plotting/_highcharts/machine_learning/tsa.py
• verticapy/plotting/_highcharts/pie.py
• verticapy/plotting/_matplotlib/acf.py
• verticapy/plotting/_matplotlib/animated/bubble.py
• verticapy/plotting/_matplotlib/animated/pie.py
• verticapy/plotting/_matplotlib/bar.py
• verticapy/plotting/_matplotlib/barh.py
• verticapy/plotting/_matplotlib/base.py
• verticapy/plotting/_matplotlib/candlestick.py
• verticapy/plotting/_matplotlib/contour.py
• verticapy/plotting/_matplotlib/density.py
• verticapy/plotting/_matplotlib/heatmap.py
• verticapy/plotting/_matplotlib/hexbin.py
• verticapy/plotting/_matplotlib/line.py
• verticapy/plotting/_matplotlib/machine_learning/champion_challenger.py
• verticapy/plotting/_matplotlib/machine_learning/importance.py
• verticapy/plotting/_matplotlib/machine_learning/lof.py
• verticapy/plotting/_matplotlib/machine_learning/pca.py
• verticapy/plotting/_matplotlib/machine_learning/regression_tree.py
• verticapy/plotting/_matplotlib/machine_learning/stepwise.py
• verticapy/plotting/_matplotlib/pie.py
• verticapy/plotting/_matplotlib/range.py
• verticapy/plotting/_matplotlib/scatter.py
• verticapy/plotting/_plotly/base.py
• verticapy/plotting/_plotly/candlestick.py
• verticapy/plotting/_plotly/contour.py
• verticapy/plotting/_plotly/line.py
• verticapy/plotting/_plotly/machine_learning/importance.py
• verticapy/plotting/_plotly/machine_learning/lof.py
• verticapy/plotting/_plotly/machine_learning/tsa.py
• verticapy/plotting/_plotly/pie.py
• verticapy/plotting/_plotly/subplots.py
• verticapy/plotting/_utils.py
• verticapy/plotting/base.py
• verticapy/plotting/sql.py
• verticapy/sdk/vertica/udf/gen.py
• verticapy/sdk/vertica/udf/load.py
• verticapy/sdk/vertica/udf/utils.py
• verticapy/sql/create.py
• verticapy/sql/dtypes.py
• verticapy/sql/functions/string.py
• verticapy/sql/geo/index.py
• verticapy/sql/sys.py